Unlike a wireless base transceiver station (BTS) in a conventional antenna configuration, a BTS equipped with an adaptive phased array antenna system utilizes power more efficiently and significantly increases the signal to noise ratio of its wireless communication channels. As a result, the capacity and the coverage area of the wireless communication system are improved.
In order to achieve the highest performance, a specific vector, called a weighting vector or spatial signature, must be applied to the array of antennas in an adaptive phased array antenna system. An optimal weighting vector for an adaptive phased array antenna system is deduced from the covariance matrix of the receiving signals.
In an orthogonal frequency division multiplexing (OFDM) wireless communication system, a receiving signal is expressed as a unit of symbols. The OFDM wireless communication method divides a broadband channel into a number of narrowband channels. A narrowband channel in the OFDM wireless communication system is denoted as a subcarrier or tone. The data carried by the broadband channel is distributed among the narrowband channels. An OFDM period is a unit of time for a wireless station to transmit or receive a symbol that is composed of the signals from all narrowband subcarriers.
An OFDM symbol can be defined as one of the following: the signal received in one OFDM period or the signal received in one subcarrier of one OFDM period. Based on the 2nd definition, an OFDM communication system with N subcarriers has N OFDM symbols in one OFDM period.
There are two challenges in obtaining an optimal weighting vector from the covariance matrix in an OFDM wireless communication system. First, conventional methods for estimating an optimal weighting vector or spatial signature for an array of antennas, such as Singular Value Decomposition (SVD), are computationally expensive. In fact, computational complexity increases exponentially with an increase in the number of elements in the covariance matrix.
Second, most of the conventional methods for estimating an optimal weighting vector require the support of pilot signal or preamble symbols. The use of a pilot signal or preamble symbol increases the overhead of a wireless communication system and reduces the capacity of the communication system.
Several blind estimation techniques, such as the constant modulus (CM) criterion, are developed to reduce the overhead incurred by a pilot signal or preamble symbol. Instead of relying on a pilot signal or preamble signal with a known code sequence, the blind estimation techniques estimate a weighting vector or spatial signature based on unknown symbols. The downside of these conventional methods is that they are also computationally expensive.
As such, what is desired is a method and system for obtaining an optimal weighting vector for an adaptive phased array antenna system that involves lower computational complexity and little overhead incurred by a pilot or preamble signal.